VI enhancing compositions and newtonian lube blends

ABSTRACT

A novel composition is disclosed that is particularly useful as a lubricant viscosity index improver. The composition comprises branched C 30  -C 10000  hydrocarbons that have a branch ratio of less than 0.19 and viscosity at 100° C. between 725 cS and 15,000 cS. The novel compositions comprise the product of the oligomerization of C 6  to C 20  alpha-olefin feedstock, or mixtures thereof, under oligomerization conditions at a temperature between -20° C. and +90° C. in contact with a reduced valence state Group VIB metal catalyst on porous support. The compositions have viscosities at 100° C. between 725 cS and 15,000 cS. Using the foregoing compositions in admixture with mineral oil and synthetic lubricants provides novel lubricant blends that show an elevated viscosity index. The mixtures also show an increased stability to shear stress at high temperature with all blends notable by exhibiting Newtonian flow.

This is a division of copending application Ser. No. 07/345,606, filedon May 1, 1989, now U.S. Pat. No. 5,012,020.

This invention relates to novel hydrocarbon oligomer compositions thatexhibit superior properties as viscosity index improvement additives forlubricants. The invention also relates to novel alpha-olefin oligomersand lubricant blends produced therefrom with conventionalpoly-alpha-olefins or mineral oil lubricant basestock that show asurprising degree of shear stability and high viscosity index (VI).

BACKGROUND OF THE INVENTION

Synthetic polyalpha-olefins (PAO) have found wide acceptability andcommercial success in the lubricant field for their superiority tomineral oil based lubricants. In terms of lubricant propertyimprovement, industrial research effort on synthetic lubricants has ledto PAO fluids exhibiting useful viscosities over a wide range oftemperature, i.e., improved viscosity index (VI), while also showinglubricity, thermal and oxidative stability and pour point equal to orbetter than mineral oil. These relatively new synthetic lubricants lowermechanical friction, enhancing mechanical efficiency over the fullspectrum of mechanical loads and do so over a wider range of operatingconditions than mineral oil. The PAO's are prepared by thepolymerization of 1-alkenes using typically Lewis acid or Zieglercatalysts. Their preparation and properties are described by J. Brennanin Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, pp 2-6, incorporated hereinby reference in its entirety. PAO incorporating improved lubricantproperties are also described by J. A. Brennan in U.S. Pat. Nos.3,382,291, 3,742,082, and 3,769,363.

In accordance with customary practice in the lubricant arts, PAO's havebeen blended with a variety of additives such as functional chemicals,oligomers and high polymers and other synthetic and mineral oil basedlubricants to confer or improve upon lubricant properties necessary forapplications such as engine lubricants, hydraulic fluids, gearlubricants, etc. Blends and their additive components are described inKirk-Othmer Encyclopedia of Chemical Technology, third edition, volume14, pages 477-526, incorporated herein in its entirety by reference. Aparticular goal in the formulation of blends is the enhancement ofviscosity index (VI) by the addition of VI improvers which are typicallyhigh molecular weight synthetic organic molecules. Such additives arecommonly produced from polyisobutylenes, polymethacrylates andpolyalkylstyrenes, and used in the molecular weight range of about45,000 to about 1,700,000. While effective in improving viscosity index,these VI improvers have been found to be deficient in that the veryproperty of high molecular weight that makes them useful as VI improversalso confers upon the blend a vulnerability in shear stability duringactual applications. This deficiency dramatically reduces the range ofusefulness applications for many VI improver additives. VI enhancersmore frequently used are high molecular weight acrylics. Theirusefulness is further compromised by cost since they are relativelyexpensive polymeric substances that may constitute a significantproportion of the final lubricant blend. Accordingly, workers in thelubricant arts continue to search for additives to produce betterlubricant blends with high viscosity index. However, VI improvers andlubricant mixtures containing VI improvers are preferred that are lessvulnerable to viscosity degradation by shearing forces in actualapplications. Preferred liquids are those that exhibit Newtonianbehavior under conditions of high temperature and high shear rate, i.e.,viscosities which are independent of shear rate. To the extent that suchsought after shear stable fluids retain viscosity under high shearstress at high temperature they would provide a significant advantageover conventional mineral oil lubricants or prior art synthetichydrocarbon (PAO) lubricants. The advantage would be readilydemonstrated in applications such as internal combustion engines wherethe use of a shear stable lubricant under the high temperature, highshear conditions found therein would result in less engine wear andlonger engine life. These fluids must also retain, or improve upon,other important properties of successful commercial lubricants such asthermal and oxidative stability.

Recently, novel lubricant compositions (referred to herein as HVI-PAOand the HVI-PAO process) comprising poly-alpha-olefins and methods fortheir preparation employing as catalyst reduced chromium on a silicasupport have been disclosed in U.S. Pat. applications Ser. No. 210,434and 210,435 filed June 23, 1988, incorporated herein by reference intheir entirety. The process comprises contacting C₆ -C₂₀ 1 -alkenefeedstock with reduced valence state chromium oxide catalyst on poroussilica support under oligomerizing conditions in an oligomerization zonewhereby high viscosity, high VI liquid hydrocarbon lubricant is producedhaving branch ratios of less than 0.19 and pour point below -15° C. Theprocess is distinctive in that little isomerization of the olefinic bondoccurs compared to known oligomerization methods to producepolyalpha-olefins using Lewis acid catalyst. Their very unique structureprovides opportunities for the formulation of superior lubricant blends.

Accordingly, it is an object of the present invention to provide novel,high viscosity lubricant compositions having improved viscosity indexand shear stability from alpha-olefins that can be utilized as lubricantVI improver additives.

It is a further object of the present invention to provide novellubricant basestock blends from high viscosity, high viscosity indexHVI-PAO in conjunction with synthetic and natural petroleum lubricant.

Another object of the present invention to provide novel lubricantcompositions from high viscosity, high viscosity index PAO blends withmineral oil and/or conventional PAO lubricants whereby blends withsuperior viscosity indices and high temperature shear stability areproduced.

Yet another object of the present invention is to provide high VIautomotive engine lubricating oils that show Newtonian behavior underconditions of high temperature, high shear stress.

SUMMARY OF THE INVENTION

A novel composition has been discovered that is particularly useful as alubricant viscosity index improver. The composition comprises branchedC₃₀ -C₁₀₀₀₀ hydrocarbons that have a branch ratio of less than 0.19 andviscosity at 100° C. between 725cS and 15,000cS. The novel compositionscomprise the product of the oligomerization of C₆ to C₂₀ alpha-olefinfeedstock, or mixtures thereof, under oligomerization conditions at atemperature between -20° C. and +90° C. in contact with a reducedvalence state Group VIB metal catalyst on porous support. Thecompositions have viscosities at 100° C. between 725cS and 15,000cS. Thecatalyst preparation includes treatment by oxidation at a temperature of200° C. to 900° C. in the presence of an oxidizing gas and thentreatment with a reducing agent at a temperature and for a timesufficient to reduce said catalyst to a lower valence state.

Using the foregoing compositions in admixture with lubricants it hasbeen discovered that the resulting lubricant mixtures or blends show anelevated viscosity index. Surprisingly, the mixtures also show anincreased stability to shear stress at high temperature with all blendsnotable by exhibiting Newtonian flow.

The lubricant mixtures of the instant invention comprise the foregoingnovel compositions and liquid lubricant taken from the group consistingessentially of mineral oil, polyolefins and hydrogenated polyolefins,polyethers, vinyl polymers, polyflurocarbons, polychlorofluorocarbons,polyesters, polycarbonates, polyurethanes, polyacetals, polyamides,polythiols, their copolymers, terepolymers and mixtures thereof.

The blends of this invention may also include other additives oradditive packages such as antioxidants, dispersants, extreme pressureadditives, friction modifiers, detergents, corrosion inhibitors,antifoamants, oxidation inhibitor, pour-point depressant and other VIimprovers.

DETAIL DESCRIPTION OF THE INVENTION

In the following description, unless otherwise stated, all references toproperties of oligomers or lubricants of the present invention refer aswell to hydrogenated oligomers and lubricants wherein hydrogenation iscarried out in keeping with the practice well known to those skilled inthe art of lubricant production.

In the present invention it has been found that C₆ -C₂₀ alpha-olefinscan be oligomerized to provide unique products having high viscosityusing the catalyst for the HVI-PAO oligomerization of alpha-olefinsreferenced hereinbefore. The novel oligomers of the present invention,as with the high viscosity index polyalpha-olefins (HVI-PAO) referencedherein before, are unique in their structure compared with conventionalpolyalpha-olefins (PAO) from 1-decene and differ from the HVI-PAOoligomers in the cited reference principally in that they are of higherviscosity. A process has been discovered to produce higher viscosityoligomers from C₆ -C₂₀ alpha-olefins that retain the unique structure ofHVIPAO. Polymerization with the novel reduced chromium catalystdescribed hereinafter leads to an oligomer substantially free of doublebond isomerization. Conventional PAO, promoted by BF₃ or ALC₁₃, forms acarbonium ion which, in turn, promotes isomerization of the olefinicbond and the formation of multiple isomers. The HVI-PAO produced in thereferenced invention and in this invention has a structure with a CH₃/CH₂ ratio <0.19 compared to a ratio of >0.19 for PAO.

It has been found that the process described herein to produce the novelhigher molecular weight, or higher viscosity, HVI-PAO oligomers can becontrolled to yield oligomers having weight average molecular weightbetween 15,000 and 200,000 and number average molecular weight between5,000 and 50,000. Measured in carbon numbers, molecular weights rangefrom C₃₀ to C₁₀₀₀₀, with a preferred range of C₃₀ to C₅₀₀₀. Molecularweight distributions, defined as the ratio of weight averaged molecularto number averaged molecular weight, range from 1.00 to 5, with apreferred range of 1.01 to 4.

Olefins suitable for use as starting material in the invention includethose alpha-olefins or 1-alkenes containing from 6 to about 20 carbonatoms such as 1-hexene, 1-octene, 1-decene, 1-dodecene and 1-tetradeceneand branched chain isomers such as 4-methyl-1-pentene. Also suitable foruse are olefin-containing refinery feedstocks or effluents. However, theolefins used in this invention are preferably alpha olefinic as forexample 1-heptene to 1-hexadecene and more preferably 1-octene to1-tetradecene, or mixtures of such olefins.

Oligomers of alpha-olefins in accordance with the invention have a lowbranch ratio of less than 0.19 and superior lubricating propertiescompared to the alpha-olefin oligomers with a high branch ratio, asproduced in all known commercial methods.

This new class of alpha-olefin oligomers are prepared by oligomerizationreactions in which a major proportion of the double bonds of thealpha-olefins are not isomerized. These reactions include alpha-olefinoligomerization by supported metal oxide catalysts, such as Cr compoundson silica or other supported IUPAC Periodic Table Group VIB compounds.The catalyst most preferred is a lower valence Group VIB metal oxide onan inert support. Preferred supports include silica, alumina, titania,silica alumina, magnesia and the like. The support material binds themetal oxide catalyst. Those porous substrates having a pore opening ofat least 40 angstroms are preferred.

The support material usually has high surface area and large porevolumes with average pore size of 40 to about 350 angstroms. The highsurface area is beneficial for supporting large amounts of highlydispersive, active chromium metal centers and to give maximum efficiencyof metal usage, resulting in very high activity catalyst. The supportshould have large average pore openings of at least 40 angstroms, withan average pore opening of >60 to 300 angstroms preferred. This largepore opening will not impose any diffusional restriction of the reactantand product to and away from the active catalytic metal centers, thusfurther optimizing the catalyst productivity. Also, for this catalyst tobe used in fixed bed or slurry reactor and to be recycled andregenerated often, a silica support with good physical strength ispreferred to prevent catalyst particle attrition or disintegrationduring handling or reaction.

The supported metal oxide catalysts are preferably prepared byimpregnating metal salts in water or organic solvents onto the support.Any suitable organic solvent known to the art may be used, for example,ethanol,methanol, or acetic acid. The solid catalyst precursor is thendried and calcined at 200° to 900° C. by air or other oxygen-containinggas. Thereafter the catalyst is reduced by any of several various andwell known reducing agents such as, for example, CO, H₂, NH₃, H₂ S, CS₂,CH₃ SCH₃, CH₃ SSCH₃, metal alkyl containing compounds such as R₃ Al, R₃B,R₂ Mg, RLi, R₂ Zn, where R is alkyl, alkoxy, aryl and the like.Preferred are CO or H₂ or metal alkyl containing compounds.Alternatively, the Group VIB metal may be applied to the substrate inreduced form, such as CrII compounds. The resultant catalyst is veryactive for oligomerizing olefins at a temperature range from below roomtemperature to about 500° C. at a pressure of 0.1 atmosphere to 5000psi. In the instant invention it has been discovered that oligomers withviscosities between 725cS and 15,000cS measured at 100° C. can beprepared when the oligomerization reaction is carried out at atemperature between -20° C. and +90° C. Contact time of both the olefinand the catalyst can vary from one second to 24 hours. The catalyst canbe used in a batch type reactor or in a fixed bed, continuous-flowreactor.

In general the support material may be added to a solution of the metalcompounds, e.g., acetates or nitrates, etc., and the mixture is thenmixed and dried at room temperature. The dry solid gel is purged atsuccessively higher temperatures to about 600° for a period of about 16to 20 hours. Thereafter the catalyst is cooled down under an inertatmosphere to a temperature of about 250° to 450° C. and a stream ofpure reducing agent is contacted therewith for a period when enough COhas passed through to reduce the catalyst as indicated by a distinctcolor change from bright orange to pale blue. Typically, the catalyst istreated with an amount of CO equivalent to a two-fold stoichiometricexcess to reduce the catalyst to a lower valence CrII state. Finally,the catalyst is cooled down to room temperature and is ready for use.

The product oligomers have a very wide range of viscosities with highviscosity indices suitable for high performance lubrication use. Theproduct oligomers also have atactic molecular structure of mostlyuniform head-to-tail connections with some head-to-head type connectionsin the structure. These low branch ratio oligomers have high viscosityindices at least about 15 to 20 units and typically 30-40 units higherthan equivalent viscosity prior art oligomers, which regularly havehigher branch ratios and correspondingly lower viscosity indices. Theselow branch oligomers maintain better or comparable pour points.

The branch ratios defined as the ratios of CH₃ groups to CH₂ groups inthe lube oil are calculated from the weight fractions of methyl groupsobtained by infrared methods, published in Analytical Chemistry, Vol.25, No. 10, p. 1466 (1953). ##EQU1##

Supported Cr metal oxide in different oxidation states is known topolymerize alpha-olefins from C₃ to C₂₀ (De 3427319 to H. L. Krauss andJournal of Catalysis 88, 424-430, 1984) using a catalyst prepared byCrO₃ on silica. The referenced disclosures teach that polymerizationtakes place at low temperature, usually less than 100° C., to giveadhesive polymers and that at high temperature, the catalyst promotesisomerization, cracking and hydrogen transfer reactions. The presentinventions produce intermediate molecular weight oligomeric productsunder reaction conditions and using catalysts which minimize sidereactions such as 1-olefin isomerization, cracking, hydrogen transferand aromatization. To produce the novel intermediate molecular weightproducts suitable for use as VI improvers with other lube stock, thereaction of the present invention is carried out at a temperaturebetween -20° and +90° C. The catalysts used in the present invention donot cause a significant amount of side reactions.

The catalysts for this invention thus minimize all side reactions butoligomerize alpha-olefins to give intermediate molecular weight polymerswith high efficiency. It is well known in the prior art that chromiumoxides, especially chromia with average +3 oxidation states, either pureor supported, catalyze double bond isomerization, dehydrogenation,cracking, etc. Although the exact nature of the supported Cr oxide isdifficult to determine, it is thought that the catalyst of the presentinvention is rich in Cr(II) supported on silica, which is more active tocatalyze alpha-olefin oligomerization at high reaction temperaturewithout causing significant amounts of isomerization, cracking orhydrogenation reactions, etc. However, catalysts as prepared in thecited Krauss references can be richer in Cr (III). They catalyzealpha-olefin polymerization at low reaction temperature to produce highmolecular weight polymers However, as the references teach, undesirableisomerization, cracking and hydrogenation reaction takes place at highertemperatures needed to produce lubricant products. The prior art alsoteaches that supported Cr catalysts rich in Cr(III) or higher oxidationstates catalyze 1-butene isomerization with 10³ higher activity thanpolymerization of 1-butene. The quality of the catalyst, method ofpreparation, treatments and reaction conditions are critical to thecatalyst performance and composition of the product produced anddistinguish the present invention over the prior art.

In the instant invention very low catalyst concentrations based on feed,from 10 wt% to 0.01 wt%, are used to produce oligomers; whereas, in thecited references catalyst ratios based on feed of 1:1 are used toprepare high polymer.

The following Examples 1 and 2 illustrate the method for the preparationof the catalyst used in alpha-olefin oligomerization to produce HVI-PAOoligomers. The method is also used in the preparation of catalyst forthe present invention. Example 2 illustrates method for the modificationof a commercially available catalyst to prepare the catalyst of thisinvention.

EXAMPLE 1

1.9 grams of chromium (II) acetate Cr₂ (OCOCH₃)₄.2H₂ O (5.05 mmole)(commercially obtained) is dissolved in 50 cc of hot acetic acid. Then50 grams of a silica gel of 8-12 mesh size, a surface area of 300 m² /g,and a pore volume of 1 cc/g, also is added. Most of the solution isabsorbed by the silica gel. The final mixture is mixed for half an houron a rotavap at room temperature and dried in an open-dish at roomtemperature. First, the dry solid (20 g) is purged with N₂ at 250° C. ina tube furnace The furnace temperature is then raised to 400° C. for 2hours. The temperature is then set at 600° C. with dry air purging for16 hours. At this time the catalyst is cooled down under N₂ to atemperature of 300° C. Then a stream of pure CO (99.99% from Matheson)is introduced for one hour. Finally, the catalyst is cooled down to roomtemperature under N₂ and ready for use.

A commercial chrome/silica catalyst which contains 1% Cr on a large-porevolume synthetic silica gel is used. The catalyst is first calcined withair at 800° C. for 16 hours and reduced with CO at 300° C. for 1.5hours.

As previously described, the reduction step in the preparation of theHVI-PAO catalyst may be carried out with a variety of reducing agents,although carbon monoxide is preferred. In the following Examples 3 and4, catalyst is prepared using carbon monoxide and hydrogen as reducingagent and 1-hexene is oligomerized to produce the novel composition ofthe present invention. In both Examples 3 and 4 the oligomerization stepis conducted by mixing 1.5 grams of the catalyst with 25 grams of1-hexene and heating under nitrogen atmosphere to 60° C. for 16 hours.The viscous product is isolated by filtering out the catalyst anddistilling off unreacted starting material and low boiling fractions at100° C. at 0.lmm Hg. The oligomerization may be conducted attemperatures between -20° C. and 90° C. Table 1 shows the catalystpreparation conditions and the properties of the oligomerization productfor Examples 3 and 4.

                  TABLE 1                                                         ______________________________________                                        Example           3         4                                                 ______________________________________                                        catalyst calcined 800° C./air                                                                      800° C./air                                catalyst reduction                                                                              CO/350° C.                                                                       H.sub.2 /300° C.                           oligomer yield, wt %                                                                            84        12.5                                              Vis. @ 100° C., cS                                                                       1882      737                                               MW.sub.n, × 10.sup.3                                                                      4.53      2.9                                               MW.sub.w, × 10.sup.3                                                                      18.75     12.5                                              polydispersity, MW.sub.w /MW.sub.n                                                              4.14      4.2                                               ______________________________________                                    

The products from the oligomerization reaction contain someunsaturation. However, HVI-PAO with MW_(n) greater than 8000, orapproximately 500cS for 1-decene-based HVI-PAO, has very lowunsaturation as synthesized. Unsaturation can be reduced byhydrogenation in order to improve thermal and oxidative stability of theproduct.

The results in Table 1 show that high viscosity poly-1hexene can beproduced by the activated chromium on silica catalyst. In a similarmanner at a temperature between -20° C. and 90° C. high viscosityoligomer can be prepared for alpha-olefins from C₇ to C₂₀.

In Table 2 the results of mixing or blending the product obtained inExample 3 with a mineral oil comprising solvent-refined paraffinicneutral 100 SUS basestock is presented. The results show the significantimprovement in viscosity and VI achieved in the blend resulting from thenovel oligomer of the invention.

                  TABLE 2                                                         ______________________________________                                        Weight Percent        Viscosity, cS                                           Ex. 3 Product                                                                           Mineral Oil                                                                             100° C.                                                                            40° C.                                                                       VI                                      ______________________________________                                        100       0         1882.0      --    --                                      24.9      75.1      21.78       153.18                                                                              168                                     10.0      90.0      8.65        52.25 142                                     0         100       4.19        21.32  97                                     ______________________________________                                    

The following Example 5 demonstrates that mixed alpha-olefins can beused as starting material to produce the novel product oligomers of thepresent invention.

EXAMPLE 5

Three grams of the catalyst from Example 4 is packed in a 3/8" fixed bedreactor and a mixture of alpha-olefins comprising about 17% 1-hexene,34%1-octene, 20% 1-decene, 14% 1-dodecene and 15% 1-tetradecene w-s fedthrough the reactor at 10cc per hour at 49° C. and 350 psi. The effluentcontained 43.6% lube and 56.4% unreacted starting material which can berecycled for lube production. The lube had the following viscometricproperties: Vis. @40° C. =21497 cS, Vis. @100° C. =1552.37 cS, VI =316,pour point +-9° C.

It has been discovered that the high viscosity HVI-PAO oligomersproduced in the present invention can be blended with conventionalsynthetic polyalpha-olefins to formulate cross graded engine oils suchas SAE OW-20, OW-30, 5W-40 and 5W-50. The incorporation of quantities ofhigh viscosity HVI-PAO comprising between one and forty percent of theoverall engine oil formulation produces a cross-graded product thatexhibits a high viscosity index. It has further been discovered that theaforenoted blends are Newtonian at the high temperature (150° C.) andhigh shear rate (one million reciprocal seconds)--HTHSR--conditionscommonly encountered in internal combustion engine bearings andcurrently standardized in high shear rate tests such as the TannasTapered Bearing Simulator (TBS)--ASTM D4683 --and used in European CCMCengine oil specifications.

Newtonian SAE 5W-50 versions of high performance synthetic engine oilare produced for example with about 20% of 1046 cS@100° C. or 1073cS@100C HVI-PAO. These novel oils have HTHSR viscosities between 5.7 and6.2 cP compared to HTHSR viscosities of 4.0 cP for commerciallyavailable high performance SAE 5W-50 synthetic engine oils. Accordingly,the novel engine oil formulations incorporating high viscosity HVI-PAOcan provide better engine protection than the best currently availablecommercial products of equivalent SAE cross grade.

A Newtonian SAE OW-30 version is produced with 11.5% of 1073 cS@100CHVI-PAO. This oil has an HTHSR viscosity of 3.7 cP, exceeding thecurrent lower limit of 3.5 cP set in Europe by CCMC. This limit cancurrently only be met by SAE 5W-30 synthetic formulations and SAE OW 40mineral oil formulations. Accordingly, the above type of novel SAE OW-30engine oil formulation incorporating high viscosity HVI-PAO can provideengine protection equivalent to those mineral and synthetic engine oilswhich meet current minimum European HTHSR viscosity requirements whileproviding considerably improved fuel economy and better low temperatureperformance.

Further, a Newtonian SAE OW-20 version is produced with 8.4% of 1073 cSHVI-PAO. This oil has an HTHSR viscosity of 3.0 cP, exceeding current USengine builders informally imposed lower HTHSR viscosity limits of2.6-2.9 cP. Such a formulation incorporating high viscosity HVI-PAOwould provide adequate engine protection in US built cars whileproviding considerably improved fuel economy and better low temperatureperformance compared with current commercial products meeting the sameHTHSR requirement.

The novel engine oil formulations of the present invention include, inaddition to high viscosity HVI-PAO, synthetic PAO as commerciallyobtained from the oligomerization of 1-decene with BF3 or AlC₁₃ However,other lubricants may be used in addition to PAO or in substitutionthereof. The formulations also include a typical, commercial additivepackage consisting of esters and such additives as antioxidants, ashlessdispersants and antiwear agents. For the synthetic oils above, theadditive package comprises about 33% of the formulation. In mineral oilbased formulations, the concentration would generally be lower. Thebeneficial results of the blends of the present invention can berealized using HVI-PAO from 100 cS to 20000 cS at 100C and the blendscan include between 1 and 40% of the novel HVI-PAO. To those skilled inthe art of lubricant formulation it is known that higher molecularweight, i.e. higher viscosity HVI-PAO, may be used at lowerconcentrations to achieve the VI improvement desired. But thisconsideration in formulation must be weighed against any possible lossin shear stability that generally accompanies the use of highermolecular weight VI improver, such as HVI-PAO.

The following Table 3 presents formulations for SAE viscosity gradesOW-20, OW-30 and 5W-50 of synthetic engine oil incorporating the HVI-PAOof the present invention. From the HTHSR dynamic viscosity results it isevident that the Tannas TBS (ASTM D4683) and Cannon Capillary (ASTM D4624) Viscometer results are equivalent. It can also be seen that forall the examples, the high shear rate dynamic viscosity equals the lowshear rate dynamic viscosity, determined from the product of kinematicviscosity measured at 150° C. and the density projected to 150° C. bythe API method from room temperature measurements, and hence theseformulations are Newtonian at the HTHSR conditions.

Although the HVI-PAO examples cited are of synthetic engine oils, itshould be understood that the same formulation principles can be appliedto any lubricant where a high VI is required with no loss of viscositydue to shear, such as hydraulic oils, aviation oils, gear oils, turbineoils, circulating oils, and the like.

Although the wide cross grades such as SAE 5W-50 and OW-30 can only bemade with high VI starting basestocks such as PAO, ester, polyglycol andXHVI mineral oils, lower crossgrades can be made with basestocks oflower VI such as conventional mineral oils and these will in turn haveimproved shear stability over their counterparts made by conventionalVI-improver techniques.

Among the lubricant base stocks with which the present VI improvers maybe used are the high viscosity index lubricants of mineral oil originproduced by the hydrocracking of petroleum waxes, referred to herein asXHVI lubricants. These lubricant basestocks are derived from waxes whichare separated from oils during conventional solvent dewaxing processes,especially from lubricating oil stocks including both neutral(distillate) and residual stocks. In the process for converting thewaxes to the XHVI lubestocks, the separated wax is subjected tohydrocracking at high pressure, typically at 1500-300 psig, over anamorphous catalyst such as alumina containing a metal component, usuallya base metal component such as nickel/tungsten. Processes of this kindand the products obtained are described, for example, in British PatentsNos. 1390359, 1545828, 1324034, 1429291, 1429494, to which reference ismade for a detailed description of such processes and their products.

                  TABLE 3                                                         ______________________________________                                        SAE Viscosity Grade                                                                        5W-50           OW-20   OW-30                                    ______________________________________                                        1046 cS HVI-PAO                                                                            21%     19%     --    --    --                                   1073 cS HVI-PAO                                                                            --      13      21%   8.4%  11.5%                                PAO          45.9%   47.9%   45.9  58.5% 55.4%                                Additive Package                                                                           33.1%   33.1%   33.1% 33.1% 33.1%                                cS @ 40° C.                                                                         100     87      100   40    51                                   cS @ 100° C.                                                                        18.9    16.7    18.8  8.4   10.4                                 VI (ASTM D2270)                                                                            212     210     210   193   200                                  CCS*.sup.2 @ -25° C., P                                                             34.5    30.5    --    --    --                                   CCS @ -30° C., P                                                                    --      --      --    21.5  28.3                                 HTHSR, cP    6.2     5.7     --    3.0   3.7                                  (Cannon)*.sup.3                                                               HTHSR, cP    6.2     5.5     --    --    --                                   (Tannas TBS)*.sup.4                                                           Calc. HTHSR*.sup.1 cP                                                                      6.3     5.6     --    3.0   3.7                                  Noack Volatility                                                                           --      --      11.2% --    --                                   ______________________________________                                         *.sup.1 the product of kinematic viscosity measured at 150°  C. an     density projected to 150° C. per API method.                           *.sup.2 Cold Crank Simulator (ASTM D2602 MOD).                                *.sup.3 (ASTM D4624).                                                         *.sup.4 (ASTM D4683).                                                    

In the case of blends of PAO with HVI-PAO as disclosed herein, thebasestock PAO component is obtained from commercial sources such asMOBIL Chemical Co. The commercial material is typically prepared by theoligomerization of 1-alkene in the presence of promotedborontrifluoride, aluminum chloride or Ziegler catalyst and ischaracterized by having a branch ratio greater than 0.19 and viscosityindices significantly lower than HVI-PAO. Other liquid lubricants usefulas blending components with HVI-PAO in the present invention includelubricant grade mineral oil from petroleum. Yet other useful HVI-PAOblending components include unsaturated and hydrogenated polyolefinssuch as polybutylene and polypropylene, liquid ethylene-propylenecopolymer and the like; vinyl polymers such as polymethylmethacrylateand polyvinylchloride; polyethers such as polyethylene glycol,polypropylene glycol, polyethylene glycol methyl ether; polyflurocarbonssuch as polytetrafluroethylene and polychloroflurocarbons such aspolychlorofluroethylene; polyesters such as polyethyleneterephthalateand polyethyleneadipate; polycarbonates such as polybisphenol Acarbonate; polyurethanes such as polyethylenesuccinoylcarbamate;silicones; polyacetals such as polyoxymethylene; polyamides such aspolycaprolactam. The foregoing polymers include copolymer thereof ofknown composition exhibiting useful lubricant properties or conferringdispersant, anticorrosive or other properties on the blend. In allcases, blends may include other additives.

The present invention has been described with preferred embodiments.However, modifications and variations may be employed and are consideredto be within the purview and scope of the appended claims.

What is claimed is:
 1. A process for the production of a hydrocarboncomposition useful as a lubricant viscosity index improvercomprising;contacting C₆ -C₂₀ alpha-olefins, or mixtures, thereof, underoligomerization conditions at a temperature between=20° C. and 90° C.with a reduced valence state Group VIB metal catalyst on porous support,wherein said catalyst has been treated by oxidation at a temperature of200° C. to 900° C. in the presence of an oxidizing gas and then bytreatment with a reducing agent at a temperature and for a timesufficient to reduce said catalyst to a lower valence sae; andrecovering said composition.
 2. The process of claim 1 wherein saidcatalyst comprises CO reduced CrO₃ and said support comprises silicahaving a pore size of at least 40 Angstroms.
 3. A method for theproducing of Newtonian liquid lubricant having improved viscosity index,comprising;mixing a liquid lubricant basestock with a viscosity indeximproving amount o the product of the oligomerization of C₆ to C₂₀alpha-olefin feedstock, or mixtures thereof, under oligomerizationconditions at a temperature between-20° C. and 90° C. in contact with areduced valence state Group VIB metal catalyst on porous support, saidproduct having viscosity at 100° C. support 100cS and 20,000cS; whereinsaid catalyst has been treated by oxidation at a temperature of 200° c.to 900° C. in the presence of an oxidizing gas and then by treatmentwith a reducing agent at a temperature and for a time sufficient toreduce said catalyst to a lower valance state; said newtonian liquidlubricant exhibiting shear stability under high temperature, high shearrate conditions.
 4. The method of claim 3 wherein said high temperature,high shear rate conditions comprises temperature of 150° C. and shearrate of one million reciprocal seconds.
 5. The method of claim 3 whereinsaid product has a viscosity at 100°C. of less than 2000cS.